This application is based on Japanese Patent Application No. 2001-037048, filed Feb. 14, 2001, and Japanese Patent Application No. 2001-288523, filed Sep. 21, 2001, the entire contents of both being hereby expressly incorporated by reference herein.
1. Field of the Invention
The present invention relates generally to a control system for a marine engine, and more particularly to an improved control system for a marine engine that controls an amount of fuel injected by one or more fuel injectors.
2. Description of Related Art
Relatively small watercraft such as, for example, personal watercraft have become very popular in recent years. This type of watercraft is quite sporting in nature and carries one or more riders. A hull of the watercraft typically defines a rider""s area above an engine compartment. An internal combustion engine powers a jet propulsion unit that propels the watercraft by discharging water rearwardly. The engine lies within the engine compartment in front of a tunnel which is formed on an underside of the hull. At least part of the jet propulsion unit is placed within the tunnel and includes an impeller that is driven by the engine.
Personal watercraft transfer to a planing position from a trolling position as they accelerate. Such watercraft operate at low speed in a trolling position, i.e., relying on their buoyancy to stay afloat. Typically, when such watercraft are idling or moving at a trolling speed, the majority of the lower portion of the hull is below the waterline, thereby displacing a sufficient volume of water to keep the watercraft floating.
As the watercraft accelerates, the impact of the water on the lower surface of the hull creates a reaction force that combines with the buoyant force to lift more of the watercraft out of the water, thereby transferring the watercraft from a trolling position to a planing position. As the watercraft transfers to the planing position, the bow of the watercraft rises relative to the surface of the body of water.
Once in the planing position, the watercraft is supported nearly entirely by the reaction force created by the impact of water on the lower surface of the hull, with little or no contribution from the buoyancy of the hull. As such, only a small portion of the lower hull contacts the water, thereby reducing the hydro-dynamic drag on the hull. Thus, the watercraft can move more quickly when in the planing position. Many riders prefer running personal watercraft, as well as other planing watercraft, in the planing position.
The engine can employ a fuel injection system that sprays fuel for combustion in one or more combustion chambers of the engine. Typically, amounts of sprayed fuel are controlled by a controller such as, for example, an electronic control unit (ECU) to maintain proper air/fuel ratios for good emission control and fuel economy. Known control systems use either a D-j control mode or an xcex1-N control mode for the purpose. The D-j control mode determines an amount of the injected fuel based upon a signal from an intake pressure sensor and a signal from an engine speed sensor. The xcex1-N control mode determines the amount of the injected fuel in a slightly different way and based upon a signal from a throttle valve opening degree sensor and a signal from an engine speed sensor.
One aspect of the present invention includes the realization that D-j control performs better at low engine speeds and xcex1-N control performs better at higher engine speeds. Thus, another aspect of the invention is directed to a controller for an engine which uses an intake air pressure control scenario, such as for example but without limitation, D-j control for low engine speeds operation and which uses a throttle position control scenario, such as for example but without limitation, xcex1-N control for higher engine speeds.
In an exemplary D-j control scenario, an amount of intake air is indirectly calculated based on a air pressure detected in the induction system of the engine. Predetermined data indicating a relationship between intake air pressure and the actual amount of air (the actual amount of air entering the combustion chamber) is applied to the detected air pressure. The data typically is stored as a control map. The D-j control mode additionally relies on data, which is stored as, for example, a three-dimensional map, indicating relationships among an amount of air, an engine speed, and an amount of fuel that would produce the desired air/fuel ratio. A desired fuel amount is thus based on the detected air pressure and the engine speed. The controller then causes the fuel injectors to inject the desired amount of fuel.
It has been found that although such a D-j control scenario performs well at lower engine speeds and smaller throttle openings, it does not maintain desired air/fuel ratios as well as at relatively higher engine speeds and larger throttle openings. In particular, this performance disparity is remarkable with multiple cylinder engines that employ separate throttle valves at respective intake passages. Thus, the D-j control mode preferably is used for control of the fuel amount in a relatively low speed range of the engine speed, and/or smaller throttle openings.
The controller, using the xcex1-N control scenario, in turn, calculates the amount of air entering the combustion chamber indirectly from a detected throttle valve opening size. Data indicating relationships between the throttle valve opening and an actual amount of air is applied to the detected throttle opening, thereby yielding an actual amount of air entering the combustion chamber. The xcex1-N control also utilizes data, which also is stored as, for example, another three-dimensional map, indicating relationships among an air amount, an engine speed, and an amount of fuel required to produce a desired air/fuel ratio. Thus, the desired amount of fuel is based on the throttle valve opening degree and the engine speed. The controller then causes the fuel injectors to inject the desired amount of fuel.
It has been found that the xcex1-N control scenario performs better than the D-j scenario at higher engine speeds and larger throttle openings. In particular, this performance disparity is remarkable in multiple cylinder engines that employs separate throttle valves at each respective intake passage. The xcex1-N control scenario, thus, preferably is used for control of the fuel amount at relatively high engine speeds and/or larger throttle openings.
As noted above, one aspect of the present invention is directed to a control systems that employs both D-j control and xcex1-N control and switches between these modes in response to at least one of engine speed and throttle opening.
Another aspect of the present invention includes the realization that in a vehicle with an engine that employs a system that switches between two control scenarios during operation, the behavior of the engine can change noticeably during switching. In particular, it has been found that a rider of a watercraft using such a system can experience an uneasy feeling that something is wrong with the engine when the controller switches from the D-j control mode to the xcex1-N control mode, and vice versa. Additionally, it has been found that the change in behavior is particularly noticeable during transition from a trolling position to a planing position.
Yet another aspect of the present invention includes the realization that if the intake air pressure sensor or the throttle valve position sensor malfunctions, the D-j and xcex1-N control modes, respectively, become un-usable. However, despite the performance disparity between the D-j and xcex1-N control modes, one of these control modes can be used for all engine speeds if the other is un-usable due to sensor malfunction. For example, if the intake air pressure sensor malfunctions, the xcex1-N can be used for all engine speeds. Although this control mode does not perform as well at low engine speeds and small throttle openings, it will allow the engine to operate with only minor or no changes in engine behavior that are noticeable by a rider. Similarly, if the throttle position sensor malfunctions, D-j control mode can be used for all engine speeds.
A need therefore exists for an improved control system more reliably provides a desired air/fuel ratio without producing noticeable changes in engine behavior.
In accordance with one aspect of the present invention, a watercraft includes a hull and an engine supported by the hull. The engine comprises an engine body, a fuel supply system connected to the engine and configured to supply fuel for combustion in the engine body. A first sensor is configured to detect a first engine operation parameter and a second sensor is configured to detect a second engine operation parameter. The watercraft also includes a controller configured to control at least the fuel supply system. In particular, the controller is configured to control the fuel supply system according to a first mode in a first engine speed range and to control the fuel supply system according to a second mode in a second engine speed range. Additionally, the controller is configured to control the fuel supply system according to a malfunction mode in which the first mode is used to control the fuel supply system for the second engine speed range if the second sensor malfunctions, and to use the second mode to control the fuel supply system for the first engine speed range if the first sensor malfunctions.
In accordance with another aspect of the present invention, a method for controlling an engine for a watercraft includes detecting an engine speed and determining if the engine speed is in a first engine speed range or a second engine speed range which is higher than the first speed range. The method also includes controlling fuel supply to the engine according to a first mode based on output from a first sensor when the engine speed is in the first range and controlling fuel supply to the engine according to a second mode based on output from a second sensor when the engine speed is in the second range. Additionally, the method includes detecting a malfunction of the first and second sensors, controlling fuel supply according to the first mode in the second speed range when the second sensor malfunctions, and controlling fuel supply according to the second mode in the first engine speed range when the first sensor malfunctions.